Control of solids in processing bituminous sand

ABSTRACT

The invention concerns an improvement in water separation processes for the recovery of bitumen from bituminous sand containing the same. In such processes, a fluid slurry of bituminous sand is introduced into a separation zone containing a body of water and bitumen is floated to the top of the water in the form of a froth for recovery therefrom, while sand is allowed to settle to the bottom for removal. In accordance with the invention, controlled amounts of fine solids are maintained in an intermediate layer of water in the separation zone. Between 10 and 17 weight percent fines are preferably maintained in the intermediate water layer and such fines are mostly less than 20 microns in size. The desired concentration of fines in the water layer is maintained by recycling water from the water layer back to the separation zone or to an earlier stage of the process with removal of fines from the recycle stream in response to measurements of the amounts of fines in the water layer to maintain the desired concentration of fines in the water layer. Fresh water addition to the process is minimized by removing from the process only that water which is contained in the bituminous froth and the minimum amount of water needed to withdraw solids from the process.

United States Patent Inventors App]. No. Filed Patented Assignees CONTROL OF SOLIDS IN PROCESSING BITUMINOUS SAND 9 Claims, 1 Drawing Fig.

(1.8. CI 208/11 Int. Cl ClOg l/04 Field of Search. 208/ 1 l References Cited UNITED STATES PATENTS Baillie Floyd et a1. Graybill et a1. Erskine et a1.

BITUMINOUS AND Primary ExaminerCurtis R. Davis Attorney-J. Richard Geaman ABSTRACT: The invention concerns an improvement in water separation processes for the recovery of bitumen from bituminous sand containing the same. In such processes, a fiuid slurry of bituminous sand is introduced into a separation zone containing a body of water and bitumen is floated to the top of the water in the form of a froth for recovery therefrom, while sand is allowed to settle to the bottom for removal. In accordance with the invention, controlled amounts of fine solids are maintained in an intermediate layer of water in the separation zone. Between 10 and 17 weight percent fines are preferably maintained in the intermediate water layer and such fines are mostly less than 20 microns in size. The desired concentration of fines in the water layer is maintained by recycling water from the water layer back to the separation zone or to an earlier stage of the process with removal of fines from the recycle stream in response to measurements of the amounts of fines in the water layer to maintain the desired concentration of fines in the water layer. Fresh water addition to the process is minimized by removing from the process only that water which is contained in the bituminous froth and the minimum amount of water needed to withdraw solids from the process.

I 22 WATER 67 M IX E R 7 2 4 .56 2 34 56 20 F ROTH 28 9 /4 REJECT 30 5 STEAM MONITOR "s (k a; i 2

' 4 26/ ll 52 4o 42 4 l 4 7C ,3. I Sta L i .J E L 4 CLARIFICATION U N IT 24 }-46 SLUDGE SAND r l mcs CONTROL OF SOLIDS IN PROCESSING BITUMINOUS SAND CONTROL OF SOLIDS IN PROCESSING BITUMINOUS SAND Large deposits of bituminous sand are found in various localities throughout the world. The term bituminous sand" is used herein to include those materials commonly referred to as oil sand, tar sand and the like. One of the most extensive deposits of bituminous sand occurs, for instance, in the Athabasca district of the Province of Alberta, Canada.

Typically, the composition of these sands by weight is: from about 5 percent to about 20 percent of oil; from'about l percent to about percent of water; and from about 70 percent to about 90 percent of inorganic solids. The specific gravity of the bitumen varies from about 1.0 to about 1.05. (The specific gravity of the bitumen as well as all other values of specific gravity given herein are taken at 60 F.) The major portion, by weight of the inorganic solids is fine grain quartz sand having a particle size greater than about 44 microns and less than 2000 microns. The remaining inorganic solid matter has a particle size of less than 44 microns and is referred to as fines. The fines contain clay and silt including some very small particles of sand. The fines content typically varies from about 5 percent to above 30 percent by weight of the solid inorganic content of bituminous sand. However, the composition of bituminous sand can vary from the above mentioned ranges and this is not too uncommon. Also, in mining the bituminous sand, clay, which is found in layers of varying thickness in such sand areas, may be admixed with the bitumen, thus increasing the inorganic solids content and particularly the fines content of the material to be processed.

Various methods have been proposed for separating bitumen from bituminous sand. The two best known methods are often referred to as the hot water method and the cold water method. In the former, the bituminous sand is jetted with steam or hot water and mulled with a small proportion of water at about 175 F., and the pulp is then dropped into a turbulent stream of circulating water and carried through a separation cell maintained at an elevated temperature of about 180 F. In the separation cell, entrained air causes the .oil to rise to the top in the form of a froth rich in bitumen which is then drawn off.

The so called cold water method" does not involve heating the bituminous sand other than whatever heating might be required to conduct the operation at room temperature. The process involves mixing the bituminous sand with water, soda ash and an organic solvent such as kerosene. The mixture is then permitted to settle at room temperature. A mixture of water and bitumen dissolved in the organic solvent rises to the top of the settling zone and is recovered.

1n the operation of water separation processes of the type described above, it is desirable to obtain a bituminous froth containing maximum quantities of bitumen and minimum quantities of water and solids. Removal of water and solids from the froth is difficult and expensive. On the other hand, attempts to operate the process so as to reduce the amount of solids and water contained in the froth usually result in excessive quantities of bitumen passing from the process with waste streams, thereby reducing recovery of bitumen and increasing the pollution problem associated with waste material.

It has now been found that improved recoveries of bitumen may be obtained and the pollution problems associated with waste material substantially alleviated by operating the primary separation zone of water separation processes such as those described above so that the intermediate water layer in the separation zone contains controlled amounts of fines, i.e., solids less than 44 microns. The amount of fines in the water layer is controlled by removing fines from the water layer in response to measurements of the amount of fines in the water layer. Preferably, this is accomplished by recycling a stream of water from the water layer with removal of fines from the recycle stream as desired. The degree of removal of lines from the recycle stream or the amount of recycle water treated for fines removal is varied in response to measurement of the amount of fines in the water layer or recycle stream. Between 10 and 17 weight percent (wt. percent) fines are preferably maintained in the water layer. By control of the fines content of the intermediate water layer as described herein, it is possible to avoid the use of excessive amounts of fresh water in the process and thereby avoid discharging from the process water streams contaminated with solids. Bitumen is for the most part associated with the water phase and by reducing the water content of the tailings stream as much as possible, the amount of bitumen withdrawn with the tailings is considerably reduced from normal practice. Limiting use of fresh water in the process has the additional advantage of reducing the expenses inherent in obtaining and treating fresh water for use in the process.

For a more complete understanding of the invention, reference should be had to the accompanying drawing which is a diagrammatic illustration of a suitable arrangement of apparatus for carrying out a preferred embodiment of the inven- 1011.

Referring to the drawing, bituminous sand entering through a conduit 12 may be mixed with water and steam in a mixer 14. Water may enter through a conduit 16 and steam through a conduit 18. In the mixer 14, the bituminous sand is thoroughly moistened and mixed with the water to form a thick slurry. The mixer 14 may take any suitable form such as a conventional rotating cylindrical tumbler having perforations for slurry to pass through and provision for rejecting oversizcd rocks and lumps of sand which cannot be broken down as through a conduit 20. Slurry from the mixer 14 preferably containing between about 20 and about 40 parts of water per parts of tar sand, passes through a conduit 22 where it may be further mixed with additional quantities of recycled water introduced through a conduit 24 and passed through the conduit 22 to a separation vessel 26. Fresh makeup water, in addition to that added to the slurrying unit, may be required to maintain the level of the froth-water interface 49. The level of the interface is detected by a level control device 53 such as a Foxboro d/p cell which activates valve 54 and admits fresh water through conduit 56 and thence to conduit 22 where it is admixed to the slurry. In the separation vessel 26, the slurry is allowed to settle in a body of water preferably maintained between about and about F. to form an upper froth layer 28, an intermediate water layer 30 and a lower sand layer 32. Bituminous froth is removed from the froth layer 28 through a conduit 34 as a product of the process for recovery of bitumen therefrom while sand tailings are withdrawn through a conduit 36 for disposal.

Froth removed through the conduit 34 typically contains between about 65 and about 75 wt. percent bitumen, between about 15 and about 32 wt. percent water and between about 3 and about 10 wt. percent solids, mostly in the form of fines of less than 44 inches micron size. Sand tailings withdrawn through the conduit 36 preferably contain between about 70 and about 80 wt. percent solids, between about 20 and about 30 wt. percent water and not more than about 1 wt. percent bitumen. The bitumen is for the most part associated with the water and by reducing the water content of the tailings stream as much as possible, the amount of bitumen withdrawn with the tailings is considerably reduced from normal practice. The amount of water withdrawn with the tailings is preferably just enough to fill the voids in the sand.

In operating the process as described herein to minimize loss of bitumen from the process with waste water and sand tailings, the amount of fresh water added in the slurrying step is only sufficient to provide the minimum needed for losses with froth sludge and tailings. Since the bituminous sand frequently contains between about 2 and about 8 wt. percent water to start with, it is preferred in practicing this invention thatno more than between about 20 and about 40 parts of water per 100 parts of bituminous sand be introduced into the process. As mentioned above, this water is used in forming the initial slurry, although some may be added at a later stage in the process, if desired or required for maintaining the level of the froth-water interface.

For best separation in the separation zone 26, it is preferred that the slurry transported to the separation zone contain more than the relatively small amount of water preferably used in forming the slurry. Rather than use fresh water for this purpose and thereby introduce unwanted additional water into the process, it is preferred that additional water he added as through the conduit 24 as described above and that such additional water be obtained by recycling water from the intermediate water layer 30. Such additional water is preferably recycled in sufficient quantities so that the slurry as introduced into the separation vessel comprises between about 40 and about 55 wt. percent water.

In the separation zone, as normally operated, most of the solid particles larger than about microns in size settle to the bottom and are removed with the sand tailings. Particles smaller than about 20 microns in size, however, do not settle as readily and tend to accumulate in the intermediate water layer. Typically, the solids in the intermediate water layer are about 90 percent smaller than 20 microns in size.

In normal operation, the bitumen particles rise to the surface of the separation zone where they coalesce to form a froth layer. The formation of the froth layer is in essence an inversion of an oil-in-water emulsion to a water-in-oil emulsion.

It is apparent that accumulation of large quantities of fines in the intermediate water layer 30 would eventually result in such large concentration of fines in the separation zone that increasing amounts of fines would eventually be carried off with the froth product through the conduit 34, thereby reducing the effectiveness of separation of bitumen from solids.

It has been found that as the concentration of fines in the intermediate water layer increases, the quality of the froth progressively deteriorates, and above a critical fines concentration emulsion inversion does not occur and no froth is formed. For practical purposes this renders the process inoperative.

To prevent undesirably large buildups of fines in the separation zone, while still restricting the amount of fresh water used in the process and waste water removed from the process to a bare minimum, the intermediate water layer 30 in the separation zone is treated for removal of controlled amounts of fines in order to maintain the fines content of the water layer at a desired level. This may be done either by direct treatment of water from the water layer 30 for removal of fines followed by return of such water to the water layer, or in a preferred embodiment of the invention by recycling a stream of water from the water layer 30 to an earlier stage in the process with treatment of at least a portion of the recycled water for removal of appropriate amounts of fines therefrom in response to indications of fines content of the water layer. As shown in the drawing, a stream of recycled water may be withdrawn from the water layer 30 as through a conduit 38. Some or all of this water may be recycled directly to the process as through a conduit 40, valve 42 and the conduit 24 referred to above while the remainder, if any, may be treated in a clarification zone, such as a clarification unit 44 for removal of some or all of the fines therefrom before being returned to the process through the conduit 24. Fines removed from the recycle stream in the clarification unit 44 are removed in the form of sludge as through a conduit 46.

Control of the amount of fines removed to maintain the desired fines content in the water layer 30 may be accomplished in any suitable manner. As shown in the drawing, a monitor 48 is used to monitor the fines content of a stream of water withdrawn from the water layer 30 through a conduit 50 and returned thereto through a conduit 52. The monitor 48 may take any suitable form. For instance, a conventional density measuring device, such as a Dynatrol density cell manufactured by Automation Products, Inc. may be used for this purpose. The output signal from the monitor 48 is then preferably used as indicated in the drawing to control the setting of the valve 42 to vary the amount of water passed through the valve 42 in response to the fines content of the water layer 30. Thus, if the fines content of the water layer 30 rises above the desired level, the valve 42 is at least partially closed to thereby divert more of the recycle stream through the clarification unit 44 for removal of fines therefrom. Likewise, as the fines content of the water layer 30 falls below the desired level, the valve 42 may be opened to allow additional quantities of the recycle stream to bypass the clarification unit. Additional valves, pumps, etc. may of course be used as necessary or desired.

Fines removed from the recycle stream by the clarification unit 44 are preferably those in the size range of between about 5 and about 20 microns. If centrifuging rather than cycloning is used for this purpose, the size range of fines removed may be increased to cover those particles larger than about 1 or 2 microns. whereas if settling vessels, with or without flocculating agents, are used for this purpose, the smallest size particles removed is usually in the order of 8 microns. Whichever method of fines removal is used, the residence time of the water being treated in the clarification unit should be kept to a minimum, preferably less than 1 minute, and certainly less than 1 day. Excessive residence times result in deaeration of bitumen so that bitumen settles with solids and is lost from the process with the sludge rather than being recycled with the recycle stream.

In practicing the present invention, it has been found that the desirable amount of fines in the intermediate water layer is usually between 10 and 17 wt. percent. The presence of more than 17 wt. percent fines in the water layer substantially reduces the effectiveness of the process and increases the amount of fines recovered with froth while less than 10 wt. percent fines in the water results in somewhat reduced recoveries of bitumen.

It has been suggested previously that excess water be used in the process to keep fines from accumulating in the water layer in such amounts as to render the process inoperable. This is usually accomplished by adding additional water to the process prior to the separation step, withdrawing water from the intermediate water layer, recovering additional bituminous froth therefrom in a secondary recovery process and then discarding the water from the secondary recovery process. Unfortunately, such secondary recovery processes yield a very poor secondary froth of comparatively low bitumen content and high water and solids content. This, of course, lowers the overall quality of the bituminous froth recovered as a product of the process and increases the costs of treating such froth for removal of water and solids therefrom. In addition, such secondary recovery processes usually discard treated water as waste material. This waste water contains substantial quantities of fines and disposal is difficult because of pollution of the rivers or lakes into which it may be discharged.

When practicing the present invention, a high quality of bituminous froth is maintained because no secondary froth is involved. Waste material is kept to a minimum by limiting the use of fresh water and recycling water from which fines have been removed to the process. Water removed with the sand tailings through the conduit 36 and with the sludge from the clarification unit 44 through the conduit 46 is kept to the absolute minimum necessary. Preferably, the total water content of these waste streams is just sufficient to fill the voids in the solids contained therein and is usually restricted to between about 20 and about 30 wt. percent of the combined sand tailings and sludge streams.

Application of the invention to recovery of bitumen from bituminous sand will be illustrated by the following examples:

EXAMPLE I Bituminous sand comprising 83.30 wt. percent solids, 11.74 wt. percent bitumen and 4.96 wt. percent water was mixed with hot water in the ratio l6.7 lbs. per I00 pounds bituminous sand in the mixer 14 to form an aqueous slurry comprising 10.1 wt. percent bitumen, 71.3 wt. percent solids and 18.6 wt. percent water at a temperature of 180 F. 280 lbs. per hour of this slurry together with 180 lbs. per hour of recycle water introduced through the conduit 24 and approximately 38 lbs. per hour of fresh water introduced through conduit 56 were passed to the separation vessel 26 and allowed to settle therein to form froth, water and sand tailings layers. From the upper portion of the separation vessel, 38.38 lbs. per hour of bituminous froth comprising 69.92 wt. percent bitumen, 6.12 wt. percent solids and 23.96 wt. percent water were withdrawn. Sand tailings comprising 0.45 wt. percent bitumen, 28.73 wt. percent water and 70.82 wt. percent solids were withdrawn at the rate of 267.14 lbs. per hour from the bottom of the separation vessel through the conduit 36.

The concentration of fines in the intennediate water layer 30 was monitored by passing a stream of water from the water layer through the density measuring monitor 48 via the conduits 50 and 52. The output from the monitor 48 was used to vary the amounts of water flowing through the conduit 40 and clarification unit 44. During the test, an average of 192.5 lbs. per hour of recycle water were withdrawn from the water layer through the conduit 38 and 50.9 lbs. per hour of this water passed through the conduit 40 while 141.6 lbs. per hour passed through the clarification unit 44 with a total of [80.0 lbs. per hour of the recycle water being returned to the process through the conduit 24. In the clarification unit 44, fines in excess of 2 microns were removed from the water and rejected from the process in the form of sludge removed through the conduit 46 at an average rate of 12.5 lbs. per hour and comprising 1.20 wt. percent bitumen, 67.25 wt. percent solids and 31.55 wt. percent water. The amount of water treated for removal of fines in clarification unit 44 was varied in direct response to the density measurements obtained in the monitor 48 and the concentration of fines in the water layer 30 was thus maintained at about 10.2 wt. percent.

EXAMPLE II In order to demonstrate the importance of controlling the amount of fines in the water layer 30 in accordance with the invention, the experimental run reported in example I was continued under the same operating conditions described in example I except that all of the water withdrawn from the water layer 30 through the conduit 38 was recycled via the conduits 40 and 24 with no removal of fines in the clarification unit 44. Under these conditions, froth removed through the conduit 34 totalled 37.94 lbs. per hour and consisted of 64.6 wt. percent bitumen, 25.5 wt. percent water and 9.9 wt. percent solids. Froth was thus recovered in about the same quantity as in example I but contained less bitumen, more water and about 50 percent more solids than the froth of example I.

While the invention has been described in connection with certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope ofthe invention.

We claim:

1. In a process for the recovery of bitumen from bituminous sand in which a fluid slurry of bituminous sand is introduced into a separation zone containing a body of water and in which bitumen is floated to the tope of such body of water in the form of a froth and recovered therefrom while sand is allowed to settle to the bottom of such body of water for removal therefrom, the improvement which comprises maintaining in such body of water an intermediate water layer of desired fines content by removing fines from such water layer in response to measurements of the amounts of fines in the water layer.

2. A process for recovery of bitumen from bituminous sand which comprises:

forming an a ueous slurry of bituminous sand; settling said s urry m a separation zone containing a body of water to from in such separation zone an upper layer of bituminous froth, an intermediate water layer containing fines less that 44 microns in size and a lower sand layer;

withdrawing froth from said upper froth layer and recovering bitumen therefrom;

withdrawing sand tailings from said lower sand layer;

withdrawing water from said intermediate water layer and recycling at least a portion of same to the separation zone; and

maintaining a desired concentration of fines in the intermediate water layer by removing fines from at least a portion of the water withdrawn from the intermediate water layer in response to measurements of the concentration of fines in the intermediate water layer.

3. The process of claim 2 in which at least about percent of the water removed from the intermediate water layer is, after removal of at least some fines from at least a portion thereof, recycled to the separation zone.

4. The process of claim 3 in which at least about percent of the solids maintained in the intermediate water layer are less than 20 microns in size.

5. The process of claim 2 in which the concentration of fines in the intermediate water layer is maintained between 10 and 17 wt. percent.

6. The process of claim 2 in which the fines removed from the intermediate water layer are between about 5 and about 20 microns in size and such fines are removed from the water withdrawn from the intermediate water layer by gravity separation.

7. The process of claim 6 in which the gravity separation is cyclone separation.

8. The process of claim 2 in which the sand tailings removed from the separation zone and the fines removed from the water withdrawn from the intermediate water layer contain a total of no more than about 30 wt. percent water and wherein such sand tailings, fines and bituminous froth constitute the sole products of the process.

9. The process of claim 8 in which fresh water added to the process is limited to amounts between about 20 and about 40 parts water per parts bituminous sand. 

2. A process for recovery of bitumen from bituminous sand which comprises: forming an aqueous slurry of bituminous sand; settling said slurry in a separation zone containing a body of water to form in such separation zone an upper layer of bituminous froth, an intermediate water layer containing fines less than 44 microns in size and a lower sand layer; withdrawing froth from said upper froth layer and recovering bitumen therefrom; withdrawing sand tailings from said lower sand layer; withdrawing water from said intermediate water layer and recycling at least a portion of same to the separation zone; and maintaining a desired concentration of fines in the intermediate water layer by removing fines from at least a portion of the water withdrawn from the iNtermediate water layer in response to measurements of the concentration of fines in the intermediate water layer.
 3. The process of claim 2 in which at least about 85 percent of the water removed from the intermediate water layer is, after removal of at least some fines from at least a portion thereof, recycled to the separation zone.
 4. The process of claim 3 in which at least about 90 percent of the solids maintained in the intermediate water layer are less than 20 microns in size.
 5. The process of claim 2 in which the concentration of fines in the intermediate water layer is maintained between 10 and 17 wt. percent.
 6. The process of claim 2 in which the fines removed from the intermediate water layer are between about 5 and about 20 microns in size and such fines are removed from the water withdrawn from the intermediate water layer by gravity separation.
 7. The process of claim 6 in which the gravity separation is cyclone separation.
 8. The process of claim 2 in which the sand tailings removed from the separation zone and the fines removed from the water withdrawn from the intermediate water layer contain a total of no more than about 30 wt. percent water and wherein such sand tailings, fines and bituminous froth constitute the sole products of the process.
 9. The process of claim 8 in which fresh water added to the process is limited to amounts between about 20 and about 40 parts water per 100 parts bituminous sand. 